The present invention relates generally to a medical device for monitoring cerebral spinal fluid pressure and relates more specifically to a miniature pressure sensor which transmits data by telemetry to an externally located receiver.
Intracranial pressure (ICP) monitoring and control is a vital component of neurosurgical management for individuals with brain edema due to a variety of maladies, including tumor, encephalitis, meningitis, and hydrocephalus [Ivan, Intracranial Pressure Monitoring with Fiberoptic Transducer for Children, CHILD""S BRAIN 7: 303-313]. Shunting systems provide for pressure management of ICP but are often subject to failure due to blockage and other faults. The ability to monitor ICP enables improved diagnosis and response to shunting failure, in addition to overall improved management of abnormal ICP conditions.
Systems exist which monitor ICP either through existing fluid shunting systems or through independent intraventricular access tubing. Because most of these systems are not fully implantable, the attached wires make continuous patient monitoring difficult, and cables restrict patient movement. In addition, the potential for infection through the interfacial boundary to the exterior of the patient is great with such partially implantable systems. Often, due to the simplicity of their design, most partially implantable systems are inherently inaccurate and, even if initially calibrated, easily become decalibrated.
Fully implantable monitoring systems are available but suffer from a number of serious drawbacks. Currently available systems rely solely upon internally located power supplies, i.e., batteries. However, once the batteries are exhausted, the device fails. Furthermore, currently available systems do not allow the simultaneous use of multiple pressure sensors or other physiological sensor combinations. Built-in programmable alarm capabilities which can warn of either mechanical/electronic problems or more serious physiological problems are also lacking in currently available monitoring systems.
Additionally, presently available implantable systems typically incorporate slow and noisy data transmission methods that are prone to interference from many sources, including nearby medical electronic equipment and systems.
Thus there is a need for a totally implantable ICP monitor which is not completely dependent upon an exhaustible internal power supply.
There is a further need for an implantable ICP monitor which can couple to existing fluid shunting systems as well as other internal monitoring probes.
There is still a further need for an implantable ICP monitor which is accurate and reliable and will not become decalibrated, even over extended periods of time.
Stated generally, the present invention relates to a completely implantable ICP monitor that is not totally dependent upon an exhaustible internal power supply. The monitor of the present invention can couple to existing fluid shunting systems as well as other internal monitoring probes. In addition, the monitor is accurate, reliable, and will not become decalibrated, even over extended periods of time.
Stated somewhat more specifically, the present invention is a fully implantable apparatus for monitoring intracranial cerebral spinal fluid pressure. In one particular embodiment, the apparatus comprises a pressure tranducer that monitors for intracranial pressure variations. The pressure transducer is coupled to a fluid handling system that can shunt excess cerebral spinal fluid (CSF) from the cerebral ventricles to a subcranial or extracranial space. The pressure tranducer produces an analog data signal which is then converted by electronic means to a digital pulse stream by generation of a spreading-code signal and then transmitted outside the patient by means of a radio-frequency (RF) transmitter to an external receiver. The external receiver unit can collect generated data as well as transmit programming signals to the implanted device.
One feature of the disclosed invention is its dual powering capabilities. The implanted device can receive power from an internal source, an inductive external source, or a combination thereof. Further, alarm parameters can be programmed into the device which are capable of producing an audible or visual alarm signal.
The utility of the disclosed invention can be greatly expanded by using multiple pressure sensors simultaneously or by combining sensors of various physiological types. The use of multiple sensors provides more accurate, complete information to medical personnel.
Thus it is an object of the present invention to provide an improved implantable intracranial pressure-monitoring device.
It is another object of the present invention to provide a miniaturized measuring device and transmitter that can operate even during battery failure.
It is still yet another object of the present invention to provide a monitoring device that transmits data is such a way that multiple units can be operated in close proximity.
It is another object of the present invention to provide a compact and portable monitoring receiver that would allow freedom of movement for the patient so that the patient can participate in routine, day-to-day activities.
It is still another object of the present invention to provide a means for both monitoring CSF pressure and controlling the shunt valve.
It is yet another object of the present invention to provide a miniature CSF pressure-monitoring system with programmable alarm capability that avoids the possibility of unrecognized and potential dangerous alterations in intracranial pressure or other life-threatening conditions in the monitored patient.
It is a further object of the present invention to provide a means for multi-physiological sensing capability from a single implanted device.
A further object of the present invention is to provide a method for monitoring CSF pressure in an individual which enables the relocation and repositioning of the subject without the difficulties associated with the moving and re-attachment of cables, wires and sensors.
It is an additional object of the present invention to provide a method for monitoring CSF in a patient where said method provides a reduced risk of infection associated with invasive instruments and sensors.
It is still an additional object of the present invention to provide a practical means for remote control of the implant, by either radio or ultrasonic techniques.
Other objects, features, and advantages of the present invention will become apparent upon reading the following specification, when taken in conjunction with the drawings and the appended claims. dr
FIG. 1 is a schematic representation of the miniaturized circuitry of the sensing unit and transceiver.
FIG. 2 is a representation of an implantable capsule showing an RF transmitter.
FIG. 3 is cross sectional representation of a patient depicting the implanted pressure sensing system attached to the fluid shunt and shunt valve.
FIG. 4 is an enlargement of the cross-sectional representation depicted in FIG. 3.
FIG. 5, is a sketch of the printed circuit board configuration of the energizing coil of the inductive power source.
FIG. 6 is a sketch of the inductive power pickup coil.